A Clinical Study to Evaluate the Safety and Efficacy of BCMA-GPRC5D CAR-T in Patients With Relapsed/Refractory Multiple Myeloma Who Received Three or More Lines of Therapy

Inclusion Criteria: 1. Patient or his or her legal guardian voluntarily participates in and signs an informed consent form; 2. Aged ≥ 18 years and ≤ 75 years; 3. Diagnosed as Multiple Myeloma (MM) according to the international standard for multiple myeloma (IMWG); 4. The presence of measurable disease at screening meets one of the following criteria:Serum M-protein ≥ 1.0 g/dL or Urine M-protein ≥ 200 mg/24h or diagnosed as Light-chain MM without measurable disease in serum and urine; Serum free light chain ≥ 10 mg/dL with an abnormal κ/λ ratio; 5. Patients must relapse or be refractory after three or more lines of therapy, which at least include: one Proteasome Inhibitor (PI), one Immunomodulatory Drug (IMiD), and one anti-CD38 monoclonal antibody; 6. diagnosed as relapsed/refractory disease or primary refractory disease; 7. The last treatment is ineffective, or the disease progresses within 60 days after the end of the last therapy; 8. Patients must recover from the toxicity of the last therapy (\< grade 2 by CTCAE criteria); 9. ECOG score 1-2 points and the expected survival period ≥ 3 months; 10. Liver, kidney and cardiopulmonary functions meet the following requirements: 1. Total bilirubin ≤ 1.5×ULN, alanine aminotransferase (ALT) ≤ 3 × ULN and aspartate aminotransferase (AST) ≤ 3 × ULN; 2. Serum creatinine ≤ 1.5×ULN, or creatinine clearance ≥ 60 mL/min; 3. Hemoglobin (Hb) ≥ 50 g/L without prior blood transfusion within 7 days; 4. Baseline peripheral oxygen saturation \> 92%; 5. Corrected serum calcium ≤ 12.5 mg/dL (≤ 3.1 mmol/L) or free (ionized, ionic) calcium ≤ 6.5 mg/dL (≤ 1.6 mmol/L); 6. Left ventricular ejection fraction (LVEF) \> 45%, without confirmed pericardiac effusion and abnormal electrocardiography with clinical significance; 7. Without clinically significant pleural effusion; 11. Venous access could be established; without contraindications of apheresis. Exclusion Criteria: 1. Previous diagnosis and treatment of other malignancies within 3 years; 2. Patients received previous anti-tumor therapies before apheresis including following therapies: targeted therapies, epigenetics modulation drugs, other drugs or medical devices (invasive) of clinical trials, monoclonal antibodies, cytotoxic agents, PIs, IMiDs, radiotherapy; 3. Central Nervous System (CNS) involvement; 4. Patients with Fahrenheit macroglobulinemia, POEMS syndrome, or primary AL, amyloidosis; 5. Subjects with positive HBsAg or HBcAb positive and peripheral blood HBV DNA titer is higher than the lower limit of detection of the research institution; HCV antibody positive; HIV antibody positive; CMV DNA titer is higher than the lower limit of detection of the research institution; EBV DNA titer is higher than the lower limit of detection of the research institution; 6. Patients have a severe allergic history; 7. Patiens have severe systemic diseases or poor cardiovascular, liver, kidney functions; 8. Acute or chronic graft versus host disease (GvHD) occurs within 6 months before the screening or needs be treated with immunosuppressive agents; 9. Active autoimmune or inflammatory diseases of the nervous system; 10. Patients develop oncology emergencies and need to be treated before screening or infusion; 11. Uncontrolled infections that need antibiotics treatment; 12. Exposure to hematopoietic growth factor of cells within 1-2 weeks before apheresis; 13. Exposure to Corticosteriods or immunosuppressive agents within 2 weeks before apheresis; 14. Patients receive a major surgical operation within 4 weeks before lymphodepletion or do not recover completely before the enrollment; or plan to receive a major surgical operation during the study period; 15. Live attenuated vaccine within 4 weeks before screening; 16. Patients with severe mental illness; 17. Patients are addcited to alcohol or drugs; 18. Pregnant or Lactating Women; Patients and his or her spouse have a fertility plan within two years after CAR-T cell infusion; 19. Other conditions considered inappropriate by the researcher.